Conventionally, a fuel cell vehicle (electric vehicle) mounted with a fuel cell system has been proposed. In such a fuel cell system, anode gas (fuel gas) and cathode gas (oxidant gas) are supplied to fuel cells (fuel cell stack) to generate power by an electrochemical reaction, whereby the generated power is supplied to a drive motor in a subsequent stage.
In this fuel cell vehicle, the following control is executed without stopping the operation of the entire fuel cell system at a low load such as during low speed travel or during a temporary stop (including during downhill travel) and during an operation in which power generation efficiency of the fuel cells decreases. Specifically, in such a state, a control is executed to stop power generation by the fuel cells by stopping the operation of auxiliary machines used to drive the fuel cell system such as a compressor for cathode gas directly related to power generation, set the fuel cells in an idle stop state, and drive the motor by power supply only from a secondary battery.
JP2012-89523A discloses a fuel cell system of an anode gas circulation type configured such that air (cathode gas) is intermittently supplied during an idle stop operation (idle stop state), thereby causing an output voltage or cell voltage of a fuel cell stack to pulsate within a predetermined range.
In such a fuel cell system, residual anode gas leaking from anode gas flow passages in the fuel cell stack and cathode gas in cathode gas flow passages react by the intermittent supply of the cathode gas during the idle stop operation, thereby preventing an oxygen concentration in the cathode gas flow passages from decreasing. In this way, a trouble during a return from the idle stop state to a normal power generation state can be prevented.
Further, by providing an upper limit to the output voltage or cell voltage during the idle stop operation, the deterioration of electrolyte membranes in the fuel cells can be prevented from advancing by suppressing an increase of the output voltage of the fuel cell stack caused by excessive supply of the cathode gas.